A little more info would be very helpful. For instance does the brake caliper mounting bracket come over onto the front of the rotor blocking it from just sliding it off? Or does the caliper just come off and then the rotor appear to be able to just come off?

If the bracket is in the way (comes around the rotor), there should be 2 bolts on the back side that hold it on. They are usually between 15-18mm. Take out the bolts, remove the bracket, and the rotor should come off.

If the rotor appears to be un-obstructed, then chances are the rotor is rusted/corroded onto the hub. Spray some PB blaster or WD-40 around the hub, let it soak, and then hit it with a hammer between the lug-studs.

Another form of rotor, although slightly rarer to see, has 2 screws holding the rotor onto the hub. Simply take out the screws and pull them off. Again, you may need to use WD-40 and a hammer.

If your planning on re-using the rotor, then make sure you DO NOT hit the friction area of the rotor with the hammer. If you have new rotors for it, then by all means, swing away.

Having not personally done brakes on a Tracker before, I don't know which type of the above I've listed is correct for the Trackers. Maybe a pic of the rotor with the caliper off and I could give you step by step instructions on how to take them off.

Another tip: If there are screws holding the rotor on after spraying with PB use either a manual impact or power/air. My mechanic told me to hit the screw right on the head with hammer to try to break the threads free, but even trying that I still needed and impact the get them off w/out stripping the heads.
Other than that Satty has about covered it.